The invention relates to a device for shape-forming at least one recess in a film-type material, said device featuring a die with at least one opening, at least one shaping stem that can be introduced into the opening to create the recess by shape-forming and a clamping facility for holding the film-type material fast between the clamping facility and the die.
It is known to manufacture base parts of blister packs, also called push-through packs, or other packaging containers with recesses or cups to accommodate contents, by means of deep-drawing, stretch-drawing or thermo-forming methods. These types of packaging may be made from thermoplastics or film-type composites, or laminates such as aluminum foils laminated with plastic films, or extrusion-deposited layers of thermoplastics.
If the packaging is made from metal-containing laminates, the manufacturing process may be performed using tools comprising stems, dies and clamping facilities. During the shape forming operation, the laminate is clamped fast between the die and the clamping facility. In order to create the desired recess or cup, the laminate is pushed into the die opening by the stem, whereby the laminate is deformed by local elongation. The result is that a shaped part exhibiting one or more recesses is formed out of the originally flat laminate.
In order to be able to exploit the elongation properties of the material to be thus formed, and hence to achieve recesses with a good deepening ratio i.e. large depth and small diameter, it is known from EP-A-0779143 to carry out the cold-forming deepening of metal-containing laminates in two steps. Using a first stem with a shape-forming surface of high coefficient of friction, the metal-plastic composite is pre-formed and then formed into its final shape using a second stem with a shape-forming surface of low coefficient of friction. This procedure suffers the disadvantage that two different stems have to be employed one after the other and therefore calls for a high degree of precision with respect to the positioning of both stems. In another variant, a telescopic type of two part stem is employed instead of two different stems. These stems are however complicated in design and cannot be employed for forming all the standard kinds of laminate.
The object of the present invention is therefore to provide a device of the kind mentioned above by means of which two-stage forming can be employed for deepening purposes, achieving a good deepening ratio in a simple manner.
That objective is achieved by way of the invention in that counter-stems which are displaceable at least within the die openings are situated in the die, whereby shape-forming regions of the forming stems and the counter-stems for clamping the film-shaped material can, at least in part, be superimposed on each other.
The arrangement of a shaping stem and a counter-stem according to the invention offers the significant advantage over the state-of-the-art that, in a simple manner, using two successive forming steps to create a recess or cup, first the potential for forming the base part and then the potential for forming the side walls, or vice versa, can be exploited.
In a preferred device according to the invention the counter-stems are positioned on a piston that can be displaced into the die along the forming axis.
The surface of the forming region of the shaping stem and/or the counter-stem may locally exhibit different coefficients of friction. Because of this the friction between the shaping stem or the counter-stem and the film to be shape-formed can be adjusted such that the sliding behavior of the film on the shaping surface of the shaping stem and the counter-stem can be influenced during the forming process.
The coefficient of friction of the shaping surface of the shaping stem and the counter-stem can be adjusted such that either stem is made of the appropriate material or features a corresponding coating.
A low coefficient of friction is obtained e.g. using materials such as polytetrafluorethylene, polyoxymethylene (polyacetal, POM), polyethylene or polyethylene-terephthalate, or mixtures thereof. Other materials than plastics may be considered e.g. metals such as aluminum or chrome steel, in particular also with polished surfaces. Further usable materials are e.g. ceramic layers or coatings containing graphite, boron nitride or molybdenum-sulphide.
Materials that may be employed to produce surfaces with high coefficients of friction are e.g. metals such as steel, or plastics such as polyacetal (POM), polyethylene, rubber, hard rubber or caoutchouc, including acrylic polymers. The metal surfaces may be given higher coefficients of friction e.g. by roughening.
The outer part of the forming and counter stems in the regions of the surfaces effecting the forming may be different in shape depending on the desired shape of recess or cup. In the simplest case the shaping and counter-stems are cylindrical in shape and exhibit flat bases; however, other three-dimensional shapes such as e.g. conical, pyramid, blunted cone, blunted pyramid, segments of spheres or a drum-shape are possible. At the same time, the counter-stem may also have a corresponding shape that fits to the shaping stem.
The shaping stem and/or the counter-stem may also be in two parts with a hollow cylindrical outer stem part and an inner stem part that can be slid in a telescopic manner out of the outer stem part.
In a preferred version of the device according to the invention, near a clamping area at the edges of the openings of the die and the clamping device, both the die and the clamping device exhibit a substrate of material of low coefficient of friction for guiding the film. This insures that the edge of the recess is uniformly formed and pore-free.
The device according to the invention is particularly suitable for producing recesses in a plastic-coated metal foil by means of cold forming, for example for manufacturing the bases for blister packs.
For the purposes of shape-forming with the device according to the invention, suitable metal-plastic composite films have e.g. a metal foil of 8 to 150 xcexcm, preferably 20 to 80 xcexcm. Suitable metals are e.g. steel, copper and aluminum. Preferred foils of aluminum are e.g. of 98% purity or higher, whereby in particular one may employ aluminum foils of alloys of the AlFeSi or AlFeSiMn type.
The plastics employed may be e.g. layers, films or laminate films of thermoplastics of the polyolefin, polyamide, polyester and polyvinylchloride series, whereby the films and film laminates may also be uniaxially or biaxially stretched. Typical examples of thermoplastics from the polyolefin series are polyethylenes, such as MDPE, HDPE, uniaxially and biaxially stretched polyethylenes, polypropylenes such as cast polypropylenes and uniaxially or biaxially stretched polypropylenes, or polyethylene-terephthalate from the polyester series. The thickness of the thermoplastic layer, in the form of a layer, film or film laminate, in the metal-plastic composite film may be e.g. 12 to 100 xcexcm, preferably 20 to 60 xcexcm.
The metal foils and the thermoplastics may e.g. be joined together by laminate bonding, colandering or extrusion bonding into composites. To join the layers, one may employ, from case to case, laminate bonding and bonding agents, and the surfaces to be joined may be modified by a plasma, corona or flame pre-treatment.
Examples of metal-plastic composite films that can be employed may have a first layer e.g. a film or laminate made up of the above mentioned thermoplastics, a second layer in the form of a metal foil and a third layer, e.g. a film or film laminate or an extruded layer made of the above mentioned thermoplastics. Further layers such as sealing layers may be fore-seen.
The metal-plastic composite films may exhibit on at least one of its outer facing sides or on both outer facing sides a sealing layer in the form of a sealable film or sealing lacquer. The sealing layer is situated, for reason of its function, in the outermost layer of the composite laminate. In particular, a sealing layer may be on the outside of the composite, whereby in the case of a blister pack this sealing layer should be facing the contents side in order to perform the sealing on of the lid film or the like.
Typical examples in practice of metal-plastic composite films that are formable using the device according to the invention are:
oPA25/Al45/PVC60
oPA25/Al45/oPA25
Al120/PP50
oPA25/Al60/PE50
oPA25/Al60/PP60
oPA25/Al45/PVC100
oPA25/Al60/PVC60
oPA25/Al45/PVC, PE-coated
oPA25/Al45/cPA25
oPA25/Al60/PVC100
oPA25/Al60/oPA25/EAA50
where oPA stands for oriented polyamide, cPA for cast polyamide, PVC for polyvinylchloride, PE for polyethylene, PP for polypropylene, EAA for ethyl-acrylic acid and Al for aluminum, and the numbers represent the thickness in xcexcm of the layers or films.